Radiographic image capturing system, image processor, and image processing method

ABSTRACT

A radiographic image capturing system includes the following. A capturing stand includes a holder to hold radiographic image capturing devices. A radiation irradiator irradiates the radiographic image capturing devices loaded in the holder at once. An image processor generates a plurality of images based on image data acquired by the radiographic image capturing devices. The image processor removes a streaky component residing in the generated image to correct the image. Such process includes forming a smoothed image by smoothing with a low-pass filter, and subtracting an interpolation image to extract a streaky image from the smoothing image and adding the streaky image to remove the streaky component. The smoothing includes reflecting smoothing on pixels showing a subject structure using a low-pass filter with a size larger in the horizontal direction compared to pixels other than pixels showing the subject structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the Japanese Patent Application No. 2016-125457, filed Jun. 24, 2016, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention specifically relates to a radiographic image capturing system related to capturing a long image by one-shot exposure, an image processing apparatus and an image processing method.

Description of Related Art

An example of the recently developed capturing stands for supporting radiographic image capturing devices (flat panel detectors) used for capturing radiographic images of relatively large areas of a patient, such as a full spine or a full leg (i.e., a long image) is, for example, with reference to FIG. 27A, a capturing stand 100 including a holder 101 carrying multiple radiographic image capturing devices P1 to P3 aligned along the body axis A of a patient H (in the vertical direction in FIG. 27A) (for example, refer to Japanese Patent Application Laid-Open No. 2012-045159). The number of radiographic image capturing devices P to be loaded in the holder 101 is not limited to three.

Capturing of a long image using such a capturing stand can be carried out by positioning the patient H and the holder 101 (i.e., the radiographic image capturing devices P1 to P3) and irradiating the multiple radiographic image capturing devices P1 to P3 once via the subject (i.e., patient H) with radiation from the radiation irradiator 102 (i.e., one-shot exposure).

Although not illustrated, traditional capturing of a long image is carried out by irradiating a single radiographic image capturing device P loaded in a holder with radiation multiple times from the radiation irradiator 102 while moving the radiographic image capturing devices P1 to P3 in the vertical direction. Unfortunately, the patient could move during movement of the radiographic image capturing device P together with the holder. Capturing a long image by one-shot exposure is advantageous in that such problem due to body movement does not occur.

As illustrated in FIG. 27A, capturing of a long image through a single exposure of radiation to the multiple radiographic image capturing devices loaded in the holder with a subject disposed in front of the radiographic image capturing devices is referred to as “capturing a long image by one-shot exposure”. In the layout of the multiple radiographic image capturing devices in the holder, the bottom radiographic image capturing device P is disposed closer to the radiation irradiator 102 compared to the top radiographic image capturing device P in the holder 101, as illustrated in FIG. 27A, or the multiple radiographic image capturing devices P are staggered in the holder 101 so as to be alternately adjacent to or remote from the radiation irradiator 102, as illustrated in FIG. 27B.

Besides the vertical capturing stand 100 that captures a long image by one-shot exposure of the patient H in an upright position, as illustrated in FIGS. 27A and 27B, a horizontal capturing stand, such as that illustrated in FIG. 28, may also be used to capture a long image by one-shot exposure with radiation emitted once from above a recumbent patient H on a top panel 103 disposed above a holder 101 carrying horizontally aligned radiographic image capturing devices P1 to P3.

With reference to FIGS. 27A, 27B, and 28, ends of the radiographic image capturing devices P1 to P3 loaded in the holder 101 of the capturing stand 100 for capturing a long image by one-shot exposure overlap in view from the radiation irradiator 102. Thus, the radiographic image capturing device P in front from the radiation irradiator 102 is projected on the image acquired by the radiographic image capturing device P in the back from the radiation irradiator 102.

Among the radiographic image capturing devices loaded in a holder in a capturing stand according to the present invention, the radiographic image capturing device close to the radiation irradiator is referred to as a front radiographic image capturing device, and the radiographic image capturing device remote from the radiation irradiator is referred to as a rear radiographic image capturing device, in the case of not only the holder being installed in the vertical capturing stand 100 illustrated in FIGS. 27A and 27B, but also the horizontal capturing stand 100 illustrated in FIG. 28. Thus, the front radiographic image capturing device P in the capturing stand 100 illustrated in FIG. 28 is the top radiographic image capturing device P close to the radiation irradiator 102, and the rear radiographic image capturing device P is the bottom radiographic image capturing device P remote from the radiation irradiator 102.

With reference to FIG. 29A, an image p1 acquired by the rear radiographic image capturing device P1 (see FIG. 27A) contains transverse streaky components C_(L) caused by linear structures, such as the edges of the casing and/or inner structure of the front radiographic image capturing device P2, and structural components C_(S) caused by the structures in the casing of the front radiographic image capturing device P.

With reference to FIG. 29B, an image p2 acquired by the rear radiographic image capturing device P2 contains streaky components C_(L) caused by linear structures, such as the edges of the casing and/or inner structure of the front radiographic image capturing device P3, and structural components C_(S) caused by the structures in the casing of the front radiographic image capturing device P3.

The streaky components C_(L) do not necessarily have a width of one pixel and could have a width of several pixels to several tens of pixels. The streaky components C_(L) and the structural components C_(S) in the image p1 illustrated in FIGS. 29A and 29B are depicted to contain pixels having pixel values of 0 for simplicity. Actually, the pixels of the streaky components C_(L) and the structural components C_(S) in the image p1 do not have pixel values of 0 but pixel values smaller than the original values.

As described above, the image p1 acquired by the rear radiographic image capturing device P containing the streaky components C_(L) and the structural components C_(S), especially the image p1 containing clear streaky components C_(L), cannot be precisely aligned and combined with the image p2 acquired by the front radiographic image capturing device P. Thus, the images cannot be combined to generate a long image.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention, which has been conceived to solve the problem described above, is to acquire images by one-shot exposure that can be precisely corrected and combined to generate a long image.

According to an aspect of the present invention, there is provided a radiographic image capturing system including: a capturing stand which includes a holder which is able to hold a plurality of radiographic image capturing devices; a radiation irradiator which is able to irradiate the radiographic image capturing devices loaded in the holder at once with radiation; and an image processor which generates a plurality of images based on image data acquired by the radiographic image capturing devices, wherein, an end of a front radiographic image capturing device overlaps in an anteroposterior direction with an end of a rear radiographic image capturing device in the holder in view from the radiation irradiator, the front radiographic image capturing device being a radiographic image capturing device close to the radiation irradiator among the radiographic image capturing devices loaded in the holder, the rear radiographic image capturing device being a radiographic image capturing device remote from the radiation irradiator among the radiographic image capturing devices loaded in the holder, the image processor removes a streaky component residing in the generated image to correct the image, the removal of the streaky component includes, forming a smoothed image by smoothing with a low-pass filter to perform smoothing in a horizontal direction on a region including the streaky component set in the image, and subtracting an interpolation image obtained by interpolation in a vertical direction in a region including the streaky component on the smoothing image to extract a streaky image from the smoothing image and adding the streaky image on the region including the streaky component set in the image to remove the streaky component, wherein the smoothing includes reflecting smoothing on pixels showing a subject structure, which exists in the region including the streaky component set in the image and extends in a horizontal direction, using a low-pass filter with a size larger in the horizontal direction compared to pixels other than pixels showing the subject structure.

According to another aspect of the present invention, there is provided an image processor which generates a plurality of images based on image data acquired by irradiating radiographic image capturing devices at once with radiation in a state in which an end of a front radiographic image capturing device overlaps in an anteroposterior direction with an end of a rear radiographic image capturing device in a holder in view from a radiation irradiator, the front radiographic image capturing device being a radiographic image capturing device close to the radiation irradiator among the radiographic image capturing devices loaded in holders of a capturing stand, the rear radiographic image capturing device being a radiographic image capturing device remote from the radiation irradiator among the radiographic image capturing devices loaded in the holders, the image processor including: a processor, wherein the processor removes a streaky component residing in the generated image to correct the image, wherein the removal of the streaky component includes, forming a smoothed image by smoothing with a low-pass filter to perform smoothing in a horizontal direction on a region including the streaky component set in the image, and subtracting an interpolation image obtained by interpolation in a vertical direction in a region including the streaky component on the smoothing image to extract a streaky image from the smoothing image and adding the streaky image on the region including the streaky component set in the image to remove the streaky component, wherein the smoothing includes reflecting smoothing on pixels showing a subject structure, which exists in the region including the streaky component set in the image and extends in a horizontal direction, using a low-pass filter with a size larger in the horizontal direction compared to pixels other than pixels showing the subject structure.

According to another aspect of the present invention, there is provided an image processing method performed by an image processor which generates a plurality of images based on image data acquired by irradiating radiographic image capturing devices at once with radiation in a state in which an end of a front radiographic image capturing device overlaps in an anteroposterior direction with an end of a rear radiographic image capturing device in the holder in view from a radiation irradiator, the front radiographic image capturing device being a radiographic image capturing device close to the radiation irradiator among the radiographic image capturing devices loaded in holders of a capturing stand, the rear radiographic image capturing device being a radiographic image capturing device remote from the radiation irradiator among the radiographic image capturing devices loaded in the holders, the image processing method including: removing a streaky component residing in the generated image to correct the image, the removal of the streaky component includes, forming a smoothed image by smoothing with a low-pass filter to perform smoothing in a horizontal direction on a region including the streaky component set in the image, and subtracting an interpolation image obtained by interpolation in a vertical direction in a region including the streaky component on the smoothing image to extract a streaky image from the smoothing image and adding the streaky image on the region including the streaky component set in the image to remove the streaky component, the smoothing includes reflecting smoothing on pixels showing a subject structure, which exists in the region including the streaky component set in the image and extends in a horizontal direction, using a low-pass filter with a size larger in the horizontal direction compared to pixels other than pixels showing the subject structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings, and thus are not intended to define the limits of the present invention, and wherein;

FIG. 1 illustrates the configuration of a radiographic image capturing system according to an embodiment;

FIG. 2 illustrates an example configuration of a radiographic image capturing system including multiple capturing rooms linked to at least one console;

FIG. 3 is a perspective view illustrating the exterior of a radiographic image capturing device;

FIG. 4 is a block diagram illustrating the equivalent circuit of a radiographic image capturing device;

FIG. 5 illustrates an example configuration of a sensor panel of a radiographic image capturing device;

FIG. 6 illustrates a front radiographic image capturing device and a rear radiographic image capturing device in a holder of a capturing stand;

FIG. 7 is a flowchart illustrating the image correction process according to an embodiment;

FIG. 8 illustrates an example calibration image;

FIG. 9A illustrates loading positions and dongles disposed on a holder of the capturing stand;

FIG. 9B illustrates a dongle in connection with a connector of a radiographic image capturing device;

FIG. 10 illustrates an example calibration image after adjustment of positioning and enlargement factor;

FIG. 11A is a graph illustrating a profile of an adjusted calibration image;

FIG. 11B is a graph illustrating a profile of pixel values of a pixel column in a base image;

FIG. 12 illustrates an example region of interest assigned to an area centered on a target pixel in an image;

FIG. 13A illustrates a corrected image p1 from which structural components are removed;

FIG. 13B illustrates a corrected image p2 from which structural components are removed;

FIG. 14 illustrates a flowchart of a combining process;

FIG. 15A illustrates a corrected image p1 from which structural components are removed, with a marker added to the corrected image p1;

FIG. 15B illustrates a corrected image p2 from which structural components are removed, with a marker added to the corrected image p2;

FIG. 16 illustrates an example combined image generated through combination of images p1 and p2 illustrated in FIGS. 15A and 15B, respectively;

FIG. 17A illustrates a corrected image p1 from which structural components are removed, and in which the subjects are combined;

FIG. 17B illustrates a corrected image p2 from which structural components are removed, and in which the subjects are combined;

FIG. 18A illustrates an end edge image before combination;

FIG. 18B illustrates an end edge image after combination;

FIG. 19 illustrates an example scheme for extraction of streaky components from a region R in a combined image;

FIG. 20 illustrates pixel rows Lp1 and Lp2 selected from the region R;

FIG. 21A illustrates a subject structure image when streaky components are removed by a low-pass filter with a small size;

FIG. 21B illustrates a subject structure image when streaky components are removed by a low-pass filter with a large size;

FIG. 21C illustrates a difference image between the subject structure image shown in FIG. 21A and the subject structure image shown in FIG. 21B;

FIG. 22 illustrates a modified example scheme for extraction of streaky components in a region R in a combined image;

FIG. 23 illustrates vertical smoothing;

FIG. 24 illustrates an example long image;

FIG. 25A illustrates a processed combined image;

FIG. 25B illustrates the segmentation of a combined image;

FIG. 26 is a flow chart illustrating another process of image correction;

FIG. 27A illustrates an example configuration of a capturing stand for capturing a long image by one-shot exposure;

FIG. 27B illustrates another example configuration of a capturing stand for capturing a long image by one-shot exposure;

FIG. 28 illustrates an example configuration of a horizontal capturing stand for capturing a long image by one-shot exposure;

FIG. 29A illustrates streaky components and structural components in an image acquired by the rear radiographic image capturing device caused by the front radiographic image capturing device projected on the image; and

FIG. 29B illustrates streaky components and structural components in an image acquired by the rear radiographic image capturing device caused by the front radiographic image capturing device projected on the image.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A radiographic image capturing system according to an embodiment of the present invention will now be described with reference to the accompanying drawings. FIG. 1 illustrates the configuration of a radiographic image capturing system according to this embodiment.

FIG. 1 illustrates a capturing room Ra containing only a capturing stand 51A for capturing a long image by one-shot exposure. The capturing room Ra may also contain other capturing stands, such as a vertical capturing stand 51B and a horizontal capturing stand 51C for simple radiography (see FIG. 2). That is, when there is only one capturing room Ra, the capturing stand 51A for capturing a long image by one-shot exposure should be installed in the capturing room Ra and any other additional modalities may be optionally installed in the capturing room Ra.

The basic configuration of a radiographic image capturing system 50 according to this embodiment is illustrated in FIG. 1. One capturing room Ra is connected to one console C. Alternatively, two or more capturing rooms Ra (Ra1 to Ra3) may be connected to one or more consoles C (C1 and C2) via a network N, as illustrated in FIG. 2.

In multiple capturing rooms Ra as illustrated in FIG. 2, at least one of these capturing rooms Ra should be provided with a capturing stand 51A for capturing a long image by one-shot exposure, and any other additional modality may be optionally installed in the capturing room Ra containing the capturing stand 51A and the other capturing rooms Ra. Alternatively, a capturing stand 51A for capturing long image by one-shot exposure may be installed in all of the capturing rooms Ra.

Hereinafter, the capturing stand 51A for capturing a long image by one-shot exposure may also be simply referred to as “capturing stand 51A”. FIGS. 1 and 2 illustrate upright image capturing of a patient (not shown in FIG. 2) standing in front of the capturing stand 51A for capturing a long image by one-shot exposure. Alternatively, the capturing stand 51A for capturing a long image by one-shot exposure according to the present invention may be applied to recumbent image capturing of a patient laying or sitting on a top panel above a holder carrying multiple radiographic image capturing devices, as illustrated in FIG. 28.

[Configuration of Radiographic Image Capturing System]

With reference to FIG. 1, the capturing room Ra (or at least one of the multiple capturing rooms Ra (see FIG. 2)) according to this embodiment contains a capturing stand 51A for capturing a long image in a single exposure, which can hold multiple radiographic image capturing devices P1 to P3 for capturing a long image. The capturing stand 51A includes a holder 51 a that can carry radiographic image capturing devices P1 to P3 aligned along the body axis A of a subject or patient H.

Hereafter, the radiographic image capturing devices P1 to P3 will be collectively referred to as radiographic image capturing devices P, unless they should be differentiated. With reference to FIGS. 1 and 2, loading of three radiographic image capturing devices P in the holder 51 a of the capturing stand 51A will now be described. Alternative to three radiographic image capturing devices P, two, four, or more radiographic image capturing devices P may be loaded in the capturing stand 51A in the present invention.

With reference to FIG. 1, multiple radiographic image capturing devices P are loaded in the holder 51 a such that the lower radiographic image capturing devices P (P2 and P3) are disposed closer to the radiation irradiator 52 than the higher radiographic image capturing devices P (P1 and P2). Alternatively, multiple radiographic image capturing devices P1 to P3 maybe staggered in the holder so as to be alternately close to or remote from a radiation irradiator, as illustrated in FIG. 27B.

The capturing room Ra contains the radiation irradiator 52. With reference to FIG. 1, the radiation irradiator 52 for capturing a long image is of a wide-angle radiation type that can simultaneously expose the multiple radiographic image capturing devices P1 to P3 loaded in the capturing stand 51A through a single exposure (one-shot exposure) of the patient H as the subject with radiation.

The capturing room Ra is provided with a relay 54 for relaying the communication between individual units inside the capturing room Ra and individual units outside the capturing room Ra. The relay 54 includes an access point 53 for wireless transmission of image data D and other signals from and to the radiographic image capturing devices P1 to P3. In FIGS. 1 and 2, the radiographic image capturing devices P1 to P3, which are loaded in the holder 51 a of the capturing stand 51A, as described above, can be connected to the relay 54 via cables to establish communication. The relays 54 are connected to a controller 55 of the radiation irradiator 52 and the console C.

A console 57 of the radiation irradiator 52 is installed in a front chamber (operating chamber) Rb, as illustrated in FIG. 1. The console 57 includes an exposure switch 56 to be operated by an operator or radiologist to instruct the start of radiation to the radiation irradiator 52.

The front chamber Rb is provided with the console C composed of a computer (not shown) including a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input/output interface, connected to each other via a bus. The radiographic image capturing system 50 having the configuration illustrated in FIG. 2 may include a console C disposed outside the capturing room.

The console C includes a display Ca including a cathode ray tube (CRT) or a liquid crystal display (LCD), and an input unit including a mouse and a keyboard (not shown). The console C is connected to an external or internal storage Cb including a hard disk drive (HDD). Although not illustrated, the console C is connected to a hospital info (nation system (HIS), a radiology information system (RIS), and/or a picture archiving and communication system (PACS) via a network N.

In this embodiment, the console C functions as an image processor. Hereinafter, the console C functioning as an image processor will be referred to as image processor C. Alternatively, the image processor and the console C may be provided in the form of separate units. The CPU included in the console C as the image processor may function as a processor.

[Radiographic Image Capturing Devices]

The radiographic image capturing devices P used in the radiographic image capturing system will now be described. FIG. 3 is a perspective view illustrating the exterior of a radiographic image capturing device.

The radiographic image capturing devices P according to this embodiment each includes a casing 2 accommodating radiation detectors 7 and other components described below. One of the side faces of the casing 2 is provided with a power switch 25, a selector switch 26, the connector 27 mentioned above, and indicators 28. Although not illustrated, for example, the opposite side face of the casing 2 according to this embodiment is provided with an antenna 29 (see FIG. 4) for wireless communication with external units. A cable (not shown) can be connected to the connector 27 to establish wire communication with an external unit.

FIG. 4 is a block diagram illustrating the equivalent circuit of a radiographic image capturing device. With reference to FIG. 4, multiple radiation detectors 7 are disposed in a two-dimensional array or matrix on a sensor substrate (not shown) of a radiographic image capturing device P. The radiation detectors 7 each generate an electrical charge depending on the intensity of radiation. The radiation detectors 7 are connected to respective bias lines 9, which are connected to respective connecting lines 10. The connecting lines 10 are connected to a bias power supply 14. The bias power supply 14 applies an inverse bias voltage to the radiation detectors 7 via the bias lines 9.

The radiation detectors 7 are connected to thin film transistors (TFTs) 8, which serve as switching devices and are connected to respective signal lines 6. In a scan driver 15, a power circuit 15 a supplies ON and OFF voltages to a gate driver 15 b via a line 15 c. The gate driver 15 b switches the ON and OFF voltages applied to lines L1 to Lx of scanning lines 5. The TFTs 8 are turned on in response to an ON voltage applied via the scanning lines 5 and cause the electrical charge accumulated in the radiation detectors 7 to be discharged via the signal lines 6. The TFTs 8 are turned off in response to an OFF voltage applied via the scanning lines 5 to disconnect the radiation detectors 7 and the respective signal lines 6 and cause accumulation of the electrical charges in the radiation detectors 7.

Multiple reader circuits 17 are provided in a reader IC 16 and connected to the respective signal lines 6. During the reading process of image data D, electrical charges discharged from the radiation detectors 7 flow into the reader circuits 17 via the signal lines 6, and voltage values corresponding to the electrical charges are output from amplifier circuits 18. Correlated double sampling circuits (“CDSs” in FIG. 4) 19 read the voltage values from the amplifier circuits 18 and output analog image data items D corresponding to the voltage values to the components downstream. The image data items D are sequentially sent to an A/D converter 20 via an analog multiplexer 21, converted to digital image data items D at the A/D converter 20, and then stored in a storage 23.

A control unit 22 includes a computer (not shown) provided with a CPU, a ROM, a RAM, and an input/output interface connected to a bus, and a field programmable gate array (FPGA). The control unit 22 may be composed of a dedicated controller circuit. The control unit 22 is connected to the storage 23 provided with a static RAM (SRAM), a synchronous DRAM (SDRAM), and a NAND flash memory.

The control unit 22 is connected to a communication unit 30 that establishes wired or wireless communication with external units via an antenna 29 or a connector 27. The control unit 22 is further connected to an internal power supply 24, such as a lithium ion capacitor, that supplies electrical power to the functional units including the scan driver 15, the reader circuits 17, the storage 23, and the bias power supply 14.

In this embodiment, each radiographic image capturing device P includes a sensor panel SP composed of a sensor substrate provided with multiple radiation detectors 7 and accommodated in a casing 2 (see FIG. 3). FIG. 5 illustrates an example configuration of the sensor panel and a rear view of the sensor panel SP (the face opposite from the radiation detectors 7). The front face of the sensor panel SP (provided with the radiation detectors 7) and the rear face (provided with the control unit 22) are connected via flexible circuit boards FI. The flexible circuit boards FI are each provided with a reader IC 16 (see FIG. 4) and gate ICs (not shown) constituting a gate driver 15 b.

[Processes Carried Out at Radiographic Image Capturing System During Capturing of Long Image by One-Shot Exposure]

The processes carried out at the console C and the radiographic image capturing devices P1 to P3 loaded in the holder 51 a of the capturing stand 51A during image capturing of a long image by one-shot exposure (i.e., the processes carried out before and after emission of radiation from the radiation irradiator 52 and the processes involving reading of image data D) are basically the same as known processes carried out in simple radiography, and thus, descriptions thereon are omitted.

Upon reception of image data D from the radiographic image capturing devices P1 to P3 and offset data O corresponding to an offset due to dark charges (also referred to as dark current) generated in the radiation detectors 7, the console C calculates the true image data D* by subtracting the offset data O from the image data D for each radiation detector 7 in each radiographic image capturing devices P1 to P3 by expression (1), carries out precise image processing, such as gain correction, defective pixel correction, and gradation processing corresponding to the captured site, on the calculated true image data D*, to generate images p1 to p3 for the respective radiographic image capturing devices P1 to P3 (see FIGS. 29A and 29B). For the purpose of description, the image generated from the image data of the radiographic image capturing device P3 is described as p3, but illustration is omitted.

D*=D−O   (1)

Hereinafter, an image p generated on the basis of the image data D acquired by a radiographic image capturing device P, as described above, is referred to as an image p acquired by a radiographic image capturing device P. As illustrated in FIGS. 29A and 29B, the image p acquired by the rear radiographic image capturing device P among the images p1 to p3 acquired as described above by the respective radiographic image capturing devices P1 to P3 in the holder 51 a contains transverse streaky components C_(L) caused by linear structures, such as the edges of the casing 2 and the internal structure of the front radiographic image capturing device P (streaky components caused by multiple radiographic image capturing devices overlapping in an anteroposterior direction) and structural components C_(S) caused by structures in the casing of the front radiographic image capturing device P.

In the radiographic image capturing devices P loaded in the holder 51 a of the capturing stand 51A according to this embodiment, as illustrated in FIG. 6, the upper end of the bottom front radiographic image capturing device Pb overlaps in the anteroposterior direction with the lower end of the top rear radiographic image capturing device Pa, for example.

The lower end of the image p acquired by the top rear radiographic image capturing device Pa contains streaky components C_(L) caused by the linear ends at the top end of the casing 2 b and the top of the sensor panel SPb of the front radiographic image capturing device Pb and structural components C_(S) caused by structures inside the casing, such as the reader IC 16 and the gate IC mounted on the flexible circuit board FI (see FIG. 5) mounted on the sensor panel SPb of the front radiographic image capturing device Pb. The reference signs La and Lb in FIG. 6 will be described below.

[Image Correction Process According to Present Invention]

An image correction process will now be described for the removal of the structural components C_(S) and the streaky components C_(L) from images p acquired by the radiographic image capturing devices P loaded in the holder 51 a of the capturing stand 51A of the radiographic image capturing system 50 according to this embodiment. The operation of the radiographic image capturing system 50 according to this embodiment will also be described.

As described above, the structural components C_(S) and the streaky components C_(L) are caused by the casing 2 and the internal structures of the front radiographic image capturing device P projected on the image p acquired by the rear radiographic image capturing device P in the holder 51 a of the capturing stand 51A. At the capturing stands illustrated in FIGS. 1, 27A, and 28, the image p1 acquired by the radiographic image capturing device P1 contains projections of the casing 2 and other structures of the radiographic image capturing device P2, and the image p2 acquired by the radiographic image capturing device P2 contains projections of the casing 2 and other structures of the radiographic image capturing device P3. The image p3 acquired by the radiographic image capturing device P3 at least does not contain projections of the casings 2 and other structures of the other radiographic image capturing devices P.

At the capturing stand illustrated in FIG. 27B, the image p2 acquired by the radiographic image capturing device P2 contains projections of the casings 2 and other structures of the radiographic image capturing devices P1 and P3, but the images p1 and p3 acquired by the radiographic image capturing devices P1 and P3, respectively, at least do not contain projections of the casings 2 and other structures of the other radiographic image capturing devices P.

What image p is to contain projections of the casings 2 and other structures of other radiographic image capturing devices P depends on the layout of the radiographic image capturing devices P in the holder 51 a of the capturing stand 51A. In the description below, the rear radiographic image capturing device P is referred to as the radiographic image capturing device Pa, with reference to those exemplified in FIG. 6, and the image p acquired by the radiographic image capturing device Pa contains projections of the casing 2 and other structures of the front radiographic image capturing device Pb.

[Image Correction Process]

The image correction process according to this embodiment is carried out in accordance with the flow chart illustrated in FIG. 7. In the example flow illustrated in FIG. 7, the image correction process includes removing the structural components C_(S) from the image p and then removing the streaky components C_(L) remaining in the image p. Alternatively, the streaky components C_(L) may be removed from the image p and then the structural components C_(S) remaining in the image p may be removed. The steps in the image correction process carried out in accordance with the flow chart illustrated in FIG. 7 will now be described.

[Preliminary Acquisition of Calibration Image]

A calibration image “pcal” processed in Step S1 in the flow chart in FIG. 7 will now be described. In this embodiment, a calibration image “pcal”, such as that illustrated in FIG. 8, is generated through a process similar to that for the generation of an image p, as described above. That is, at least two radiographic image capturing devices Pa and Pb are loaded in adjacent loading positions in the holder 51 a of the capturing stand 51A (i.e., the radiographic image capturing devices Pa and Pb are loaded in accordance with the layout illustrated in FIG. 6), radiation is emitted from the radiation irradiator 52 without the subject, and the calibration image “pcal” is generated based on the image data D acquired at the rear radiographic image capturing device Pa.

The calibration image “pcal” is a preliminarily captured image of the structural components C_(S) and the streaky components C_(L) caused by the radiographic image capturing device P loaded at the front position in the holder 51 a of the capturing stand 51A and projected on the image p acquired by the rear radiographic image capturing device P. Calibration images “pcal” are preliminarily generated for every radiographic image capturing device P loadable in the holder 51 a of the capturing stand 51A.

For example, calibration images “pcal” for a radiographic image capturing device P are acquired before shipment of the device P and/or after installation of the device P to a medical facility, such as a hospital. Alternatively, calibration images “pcal” may be acquired periodically or before every image capturing process. Identification information or a cassette ID of the radiographic image capturing device P is written in the header of data on the calibration image “pcal” to preliminarily establish a correspondence between the radiographic image capturing device P and the calibration image “pcal”, and this correspondence is preliminarily stored in a database stored in a storage Cb of the image processor C (see FIGS. 1 and 2) or a storage in a server (not shown).

In this embodiment, the image processor C removes the structural components C_(S) caused by the front radiographic image capturing device Pb from the image p acquired by the rear radiographic image capturing device Pa through capturing of a subject by one-shot exposure. In this removal process, the image processor C removes the structural components C_(S) caused by the front radiographic image capturing device Pb projected on the image p on the basis of the calibration image “pcal” of the front radiographic image capturing device Pb and the image p acquired by the rear radiographic image capturing device Pa.

In this embodiment, the calibration image “pcal” is used in the step of removing the structural components in the image correction process.

[Loading Positions of Radiographic Image Capturing Device]

The radiographic image capturing device P that captures the calibration image “pcal” used for the removal of structural components is identified by the image processor C through determination of which one of the radiographic image capturing devices P is loaded in front of the rear radiographic image capturing device Pa during capturing of the image p.

For example, an operator or radiologist can instruct the image processor C to input cassette IDs of the radiographic image capturing devices P loaded at respective loading positions Q1 to Q3 (see FIG. 9A described below) in the holder 51 a of the capturing stand 51A.

Although not shown, barcodes or tags, such as two-dimensional codes or radio frequency identification (RFID) tags, that include information such as the cassette IDs may be provided on the radiographic image capturing devices P, and readers may be provided at the loading positions Q1 to Q3 in the holder 51 a of the capturing stand 51A. The codes or tags on the radiographic image capturing devices P loaded to the holder 51 a by the operator or radiologist can be automatically read with the readers, and the identification information read by the readers (i.e., information on the loading positions) and the corresponding cassette IDs of the radiographic image capturing devices P loaded at the respective loading positions can be sent to the image processor C.

With reference to FIG. 9A, dongles Do1 to Do3 that store respective identification information items are disposed at loading positions Q1 to Q3, respectively, in the holder 51 a of the capturing stand 51A. With reference to FIG. 9B, the dangles Do are connected to connectors 27 provided on the respective radiographic image capturing devices P before the radiographic image capturing devices P are loaded to the holder 51 a. Once a dongle Do is connected to a radiographic image capturing device P, the radiographic image capturing device P may read the identification information on the dangle Do (i.e., information on the loading positions) stored in the same dongle Do and send this information together with the cassette ID of the radiographic image capturing device P to the image processor C.

[Calculation of Position and Enlargement Factor of Calibration Image—Step S1]

The image processor C determines the image p to be corrected, i.e., the image p acquired by the rear radiographic image capturing device Pa, on the basis of the configuration of the holder 51 a of the capturing stand 51A (i.e., the configuration illustrated in FIG. 1 or 27B) and the information on the loading positions Q1 to Q3 of the respective radiographic image capturing devices P1 to P3. Image correction is carried out on all of the images p acquired by the rear radiographic image capturing device Pa (for example, the two images p acquired by the respective radiographic image capturing devices P1 and P2 in FIG. 1, or the image p acquired by the radiographic image capturing device P2 in FIG. 27B).

The image processor C identifies the radiographic image capturing device Pb loaded in front of the rear radiographic image capturing device Pa, which captured the image p from which the structural components are to be removed, on the basis of the configuration of the holder 51 a of the capturing stand 51A and the information on the loading positions Q of the radiographic image capturing devices P, and acquires the calibration image “pcal” for the identified radiographic image capturing device Pb.

The positional relationship between the front radiographic image capturing device Pb and the rear radiographic image capturing device Pa (i.e., the distance La between the lower end of the sensor panel Spa of the rear radiographic image capturing device Pa (corresponding to the lower end of the image p) and the upper end of the casing 2 b of the front radiographic image capturing device Pb and the distance Lb between the sensor panels Spa and SPb of the respective radiographic image capturing devices Pa and Pb, as illustrated in FIG. 6) during capturing of the calibration image “pcal” does not necessarily coincide with the positional relationship between the rear radiographic image capturing device Pa and the front radiographic image capturing device Pb during the actual capturing of a long image by one-shot exposure.

Although not shown, the distance SIDcal between the radiation irradiator 52 and the radiographic image capturing device Pa (Pb) during capturing of the calibration image “pcal” also does not always coincide with the distance SIDreal between the radiation irradiator 52 and the radiographic image capturing device Pa (Pb) during the actual capturing of a long image by one-shot exposure (see FIG. 1).

The image processor C adjusts the position of the image p and the position of the calibration image “pcal” to match each other on the basis of the information on the distances La and Lb during capturing of the calibration image written in the header of the calibration image “pcal” and the distances La and Lb during actual capturing of a long image by one-shot exposure. The adjustment of the positions can be carried out not only in the vertical direction (distance La) and the anteroposterior direction (distance Lb) but also in the transverse direction orthogonal to these directions.

The image processor C adjusts the enlargement factor of the calibration image “pcal” to match the enlargement factor of the image p on the basis of the distance SIDcal during capturing of the calibration image and the distance SIDreal during capturing of a long image by one-shot exposure, to generate an adjusted calibration image “pcal*”, as illustrated in FIG. 10.

[Removal of Structural Components—Step S2]

The image processor C removes the structural components from the image p. In the removal of the structural components, the image processor C corrects the image p by appropriately increasing the pixel values f of the image p that are reduced due to the projection of structures, such as ICs, of the front radiographic image capturing device Pb (corresponding to an area in the image p containing the structural components C_(S)) through application of the base image “ppanel”, to remove the structural components C_(S) from the image p.

Specifically, the image processor C generates a corrected image p by the following expression (2):

g(x,y)=f(x,y)+A(x,y)×k(x,y)   (2)

where f(x,y) is a pixel value of a pixel (x,y) in the image p, k(x,y) is a pixel value of a pixel in the base image “ppanel”, A(x,y) is a coefficient, and g(x,y) is a pixel value of a pixel in the corrected image p.

The image processor C generates a corrected image p by preparing a base image “ppanel” as described below. Specifically, the average value “have” is calculated as described above for the pixel values h(x,y) of the pixels in the area without streaky components C_(L) and structural components C_(S) in the adjusted calibration image “pcal*” (i.e., the top area in the image “pcal*” illustrated in FIG. 10), and the pixel values k(x,y) of the pixels in the base image “ppanel” are calculated by expression (3) for each pixel (x,y) in the adjusted calibration image “pcal*” containing the streaky components C_(L) and the structural components C_(S):

k(x,y)=have−h(x,y)   (3)

where h(x,y) is a pixel value of a pixel (x,y) in the adjusted calibration image “pcal*” (see FIG. 10).

Regarding the pixel values h(x,y) and k(x,y) in a pixel column in the adjusted calibration image “pcal*” (for example, a pixel column having a width of one pixel extending in the vertical direction as illustrated in FIG. 10) and a pixel column in the base image “ppanel”, the pixel values h(x,y) of the adjusted calibration image “pcal*” substantially equal the average value “have” in areas without streaky components C_(L) and structural components C_(S) but are smaller than the average value “have” in the areas containing the streaky components C_(L) and the structural components C_(S), as illustrated in FIG. 11A, whereas the pixel values h(x,y) of the base image “ppanel” are substantially zero in areas without streaky components C_(L) and structural components C_(S) but are positive values in the areas containing the streaky components C_(L) and the structural components C_(S), as illustrated in FIG. 11B.

The inventors have conducted a research and discovered that a mere increase in the pixel values through addition of the pixel values k(x,y) of the pixels in the base image “ppanel”, which are calculated as described above, and the pixel values f(x,y) of the pixels in the image p, as calculated by expression (4), cannot completely remove the edge components in the structural components C_(S) (i.e., the boundary between the structural components C_(S) and other areas) and results in visibly noticeable edge components remaining in the corrected image p.

g(x,y)=f(x,y)+k(x,y)   (4)

In this embodiment, the pixel values k(x,y) of the pixels in the base image “ppanel” to be added to the pixel values f(x,y) of the pixels in the image p are multiplied by the coefficient A(x,y), which varies depending on the intensity of the edge components of the structural components C_(S) (i.e., the variation in the pixel values at the boundary between the structural components C_(S) and other areas), before addition to the pixel values f(x,y) of the pixels in the image p, as defined by expression (2), to precisely remove the structural components C_(S) from the corrected image p.

The image processor C calculates the coefficient A(x,y) by assigning a region of interest (ROI) of 100 by 100 pixels centered on one of the pixels (x,y) (i.e., a target pixel (x,y)) in the image p, as illustrated in FIG. 12, for example. The image processor C calculates evaluation functions e(x,y) for the pixels (x,y) in the ROI by expression (5), and defines the coefficient A(x,y) as the minimum sum of the evaluation functions e(x,y) of the pixels (x,y) in the ROI.

e(x,y)={g(x+1,y)−g(x−1,y)}² +{g(x,y+1)−g(x,y−1)}²   (5)

The image processor C shifts the ROI in the image p and calculates the coefficients A(x,y) for the pixels (x,y) in the image p. The actual correction of the pixel values f(x,y) of the pixels in the image p by the expression (2) is only required in areas containing structural components C_(S) and streaky components C_(L). Thus, the coefficients A(x,y) should only be calculated for such areas.

The area containing the structural components C_(S) and the streaky components C_(L) can be predetermined in the calibration image “pcal” to determine the area in which the position and enlargement factor in the calibration image “pcal” are adjusted as described above, i.e., the area in the image p containing the structural components C_(S) and the streaky components C_(L). In this embodiment, the area in the image p containing the structural components C_(S) and the streaky components C_(L) are determined, and an ROI is assigned to the pixels in the areas.

That is, in this embodiment, the image processor C removes the structural components by calculating the values k(x,y) (i.e., the base image “ppanel”) to be added to the pixel values f(x,y) of the pixels (x,y) in areas in the image p containing the structural components C_(S) (see FIG. 12) based on the calibration image “pcal*” (see FIG. 10). The image processor C removes the structural components by calculating the corrected pixel values g(x,y) by adding the product of the coefficients A(x,y) and the corresponding values k(x,y) to the pixel values f(x,y), as defined by expression (2).

For the determination of a coefficient A(x,y), an ROI containing a target pixel (x,y) is assigned in the image p, as illustrated in FIG. 12. The coefficient A(x,y) is then defined as the minimum sum of the values e(x,y) (i.e., the intensity of the edge component) calculated by expression (5) (i.e., the evaluation factors) in the ROI.

In this embodiment, the image processor C removes the structural components as described above. Such a configuration allows appropriate correction of the image p and precise removal of the structural components C_(S) from the image p.

At this point, complete removal of the streaky components C_(L) is not accomplished, and some streaky components C_(L) remain in the corrected image p. Thus, in this embodiment, the image processor C removes the streaky components C_(L) remaining in the corrected image p in a subsequent step (Step S6 in FIG. 7).

[Correction of Concentration—Steps S3 and S4]

In this embodiment, the image processor C removes the streaky components C_(L) from the image p corrected as described above by temporarily combining the corrected images p1 and p2 from which the structural components C_(S) are removed as described above, the images p1 and p2 being respectively acquired by radiographic image capturing devices P1 and P2 vertically adjacent in the holder 51 a of the capturing stand 51A, as illustrated in FIGS. 13A and 13B.

Specifically, the image processor C corrects the concentration of the images p1 and/or p2 such that the concentration of the images p1 and p2 match each other (Step S3 in FIG. 7), adjusts the positional relationship and the enlargement factors of the images p1 and p2 (Step S4), performs further correction (Step S5), and overlays the identical regions of the subject in the images p1 and p2, to smoothly connect the images p1 and p2.

Known schemes may be applied to the correction of concentration, and the adjustment of positions and enlargement factors (Steps S3 to S5). Details of such schemes are disclosed in Japanese Patent Application Laid-Open Nos. 2002-44413, 2002-85392, and 2002-94772, for example. The techniques described in these specifications are processes on images captured by computed radiography (CR) cassettes. These techniques can also be effectively applied to processes of correction of concentration, and the adjustment of positions and enlargement factors in the images p captured by the radiographic image capturing devices P.

In a case where a radiographic image capturing device P3 is loaded at a loading position Q3 in the holder 51 a of the capturing stand 51A, the radiographic image capturing devices P1 and P2 are not projected on the image p3 captured by the radiographic image capturing device P3. Thus, the image p3 should not require removal of structural components. After the concentration is corrected (Step S3) and the positions and enlargement factor are adjusted (Step S4), the images p1, p2, and p3 are combined in step S5.

[Combining Process—Step S5]

When the correction of concentration, and the adjustment of positions and enlargement factors is performed on the images p1 and p2 obtained by the radiographic image capturing devices P1 and P2 adjacent to each other in the vertical direction (although image p3 is also a target when there is a radiation image capturing device P3, this is omitted in the combining process described below), the image processor C performs the combining process of the images p1 and p2.

FIG. 14 is a flowchart illustrating a combining process performed by the image processor C.

The image processor C performs the combining process by automatically selecting between two processes, a first process in which the positions of the images p1 and p2 are matched based on a position of a marker m generated in both combining target images p1 and p2 obtained from the two radiographic image capturing devices P1 and P2, and a second process in which the positions of the images p1 and p2 are matched by finding a common portion of the subject image without depending on the marker m and matching the common portion.

That is, as shown in FIG. 14, the marker m is searched in the two combining target images p1 and p2 (step S21), and when the marker m is found (step S22; YES), the combining process is performed by selecting a first process, and the positions of the two images p1 and p2 are matched by the marker m (step S23).

When the marker m is not found (step S22; NO), the combining process is performed by selecting the second process, and the positions of the two images p1 and p2 are matched with the common portion of the subject image (step S24).

Next, details of the first process using the marker m is described with reference to FIG. 15A and FIG. 15B.

The marker m is attached to a position which is a front face of the holder 51 a of the capturing stand 51A and which is in front of a portion where the portion near the lower end of the sensor panel SP of the radiographic image capturing device P1 overlaps with the portion near the upper end of the sensor panel SP of the radiographic image capturing device P2.

The marker m is a member formed from a material with high absorptivity of radiation and with a known front view shape and size. The marker m is set to a size which does not disturb capturing of the subject.

The marker m is detachable from the capturing stand 51. When the above-described second process is selected, the subject is imaged without attaching the marker m to the capturing stand 51.

When the subject is captured with the marker m attached to the capturing stand 51, the image p1 shown in FIG. 15A and the image p2 shown in FIG. 15B can be obtained by the radiographic image capturing devices P1 and P2.

As illustrated in the drawing, in the image p1, the marker m appears at both ends in the horizontal direction in the lower end, and in the image p2, the marker m appears at both ends in the horizontal direction in the upper end. As shown in FIG. 15A and FIG. 15B, preferably, two or more markers m are used to match the positions of the two images p1 and p2.

The image processor C performs the search of the marker m appearing in the images p1 and p2. As described above, since the shape and size of the marker m are known, data of the template image showing the marker m is prepared in advance in the storage such as the non-volatile memory and the HDD included in the image processor C, and the marker m is searched using a well-known template matching method. Since the marker m is positioned in the region near the lower end in the image p1 and the region near the upper end in the image p2, preferably, the search region is limited to a range of the images p1 and p2 suitably defined for each image.

Then, when two markers m are found in each of the images p1 and p2, the central position of the marker m is obtained, and the pixel position of the central position of the marker m in each of the images p1 and p2 is stored. The process of searching the markers m by the template matching method corresponds to the process in steps S21 and S22 according to the above-described flowchart shown in FIG. 14.

Then, as shown in FIG. 16, the two images p1 and p2 are spread on a common planar coordinate system. The image p2 is moved and rotated (the image p1 may be moved and rotated) so that the central position of the marker m in one end in the horizontal direction and the central position of the marker m in the other end in the horizontal direction respectively match. With the central positions of the two markers m matching, the images p1 and p2 are combined with a portion of the lower end of the image p1 overlapping with a portion of the upper end of the image p2. With this, the long image plong* is formed.

Next, details of the second method used in the common portion of the subject image are described with reference to FIG. 17A and FIG. 17B. The second method is performed when the marker m cannot be found in the images p1 and p2.

First, the image processor C spreads the two images p1 and p2 on the common planar coordinate system and extracts a portion of the end image to be combined for each of the images p1 and p2. Here, the end image of either one of the images p1 and p2 is to be the search region, and the other end image is to be the search target. Therefore, the one end image is largely extracted than the other end image. Here, as shown in FIG. 17A, an end image pt1 of the image p1 is to be the search region and as shown in FIG. 17B, an end image pt2 of the image p2 is to be the search target.

Preferably, the end image pt1 extracted as the search region is extracted including the image showing the horizontal direction of the radiographic image capturing apparatus 1. For example, the edge of the lower end in the image p1 and the streaky component C_(L) are horizontal and the image is extracted in the range including the streaky component C_(L).

As shown in FIG. 18A, the image processor C filters the extracted end images pt1 and pt2 with edge detecting filters and generates end edge images pte1 and pte2.

Further, an inclination angle of the image p1 with respect to the image p2 is detected from the streaky component C_(L) of the end edge image pte1 (strictly, the extracted edge of the streaky component C_(L)).

Then, according to the detected inclination angle, rotation is performed so that the inclination angle of the end edge image pte1 is corrected. The end edge image pte2 is roughly positioned in an overlapping position with respect to the end edge image pte1. Then, fine positioning is performed so that the end edge image pte2 matches with the end edge image pte1.

That is, the images are moved separately in very fine units (for example, one pixel at a time) in the horizontal direction and the vertical direction, and the degree of matching is determined by the pattern matching method each time. Here, as one example, the degree of matching is calculated by cross correlation method. According to the cross correlation method, the pixel value for each pixel of the end edge image pte1 in which the position of each pixel in the end edge image pte2 overlaps is multiplied separately, and the sum of the above is calculated. When the sum is a predetermined threshold or more, it is determined that the end edge image pte2 matches with the end edge image pte1 (state of FIG. 18B). Then, the movement amount and the movement direction of the matched end edge image pte2 are recorded.

Then, based on the inclination angle obtained from the streaky component C_(L) of the end edge image pte1 and the movement amount and the movement direction of the end edge image pte2 obtained from the cross correlation method, the image p2 is moved and rotated (the image p1 can be moved and rotated), and the images p1 and p2 are combined with a portion of the lower end of the image p1 and a portion of the upper end of the image p2 overlapped. With this, the long image plong* (image with the marker m removed from the long image plong* shown in FIG. 16) is formed.

In a typical process of generating a long image “plong” through combination of two images, the connecting area of the two images (overlapping area) contains only the image captured by the radiographic image capturing device Pb, which is loaded at the front position in the holder 51 a of the capturing stand 51A (for example, the image captured by the front radiographic image capturing device Pb in FIG. 6), and does not contain the image captured by the rear radiographic image capturing device Pa, which is loaded at the rear position in the holder 51 a of the capturing stand 51A, because the front radiographic image capturing device Pb may be projected on the connecting area (overlapping area) in the image captured by the rear radiographic image capturing device Pa.

In this embodiment, the images p1 and p2 are temporarily combined to remove the streaky components. Thus, in the step of combining the images (Step S5), the connecting area (overlapping area) of the images p1 and p2 to be combined contain the remaining streaky components C_(L) captured by the radiographic image capturing devices P loaded in the rear positions in the holder 51 a of the capturing stand 51A (i.e., the radiographic image capturing devices P1 and P2 respective to the radiographic image capturing devices P2 and P3), unlike the images used in the process described above.

In this embodiment, the combined image “plong*” contains a streaky component C_(L) remaining in the image p1 in the connecting area (overlapping area) of the two images (for example, images p1 and p2), as illustrated in FIG. 16. Although not shown, the connecting area of the images p2 and p3 (overlapping area) also contains streaky components C_(L) that remained in the image p2.

Hereinafter, an image acquired through combination of images p, as described above, is referred to as combined image “plong*” for differentiation from a long image “plong” combined through a typical scheme.

[Removal of Streaky Components (Basic Type)—Step S6]

The image processor C removes the streaky components C_(L) residing or remaining in the combined image “plong*” on the basis of the combined image “plong*” generated as described above (Step S6 in FIG. 7). The removal of the streaky components C_(L) from the connecting area of the images p1 and p2 of the combined image “plong*” (see FIG. 16) will now be described. The streaky components C_(L) in the connecting area of the images p2 and p3 are also removed in a similar process.

In this embodiment, the streaky components are removed as follows. The streaky components C_(L) can be regarded as horizontal low-frequency components (along the y direction in FIG. 16) in the combined image “plong*”. With reference to FIG. 19, the image processor C extracts a region R containing the streaky components C_(L) in the combined image “plong*”, applies a low-pass filter, such as a Gaussian filter, in the horizontal direction of the region R (i.e., a pixel row having a width of one pixel extending in the horizontal direction), and smooths the streaky components C_(L) along the horizontal direction.

As described above, the area containing the streaky components C_(L) in the combined image “plong*”, i.e., the area containing the streaky components C_(L) in the image p1, can be determined on the basis of the area containing the streaky components C_(L) in the calibration image “pcal”. Thus, the region R in the combined image “plong*” containing the streaky components C_(L) can be assigned to a region equivalent to the area containing the streaky components C_(L) plus a predetermined number of pixels added to the top and bottom edges, for example.

Smoothing of the streaky components C_(L) through the low-pass filter can be controlled and varied on the basis of information on the subject and edges in the pixel rows to be smoothed.

The region R of the combined image “plong*” passing through the low-pass filter along the horizontal direction contains the smoothed streaky components C_(L) superimposed on background DC components. Thus, the image processor C extracts the DC component from the region R of the combined image “plong*” after passing the combined image “plong*” through the low-pass filter.

Specifically, with reference to FIG. 20, the image processor C selects pixel rows Lp1 and Lp2, each having a width of one pixel, from areas above and below a region Rc containing the streaky components C_(L), in other words a region Rc other than the region containing the streaky components C_(L), within the region R containing the streaky components C_(L), in the combined image “plong*” passing through the low-pass filter.

The image processor C performs linear interpolation by expression (6), for example, on pixel values g(x,y) upper of pixels in the upper pixel row Lp1 and corresponding pixel values g(x,y) lower of pixels in the lower pixel row Lp2 (i.e., pixels on different pixel columns at the same y coordinates), to calculate the pixel values g*(x,y) of the pixels between the pixel rows Lp1 and Lp2.

g*(x,y)=t×g(x,y)upper+(1−t)×g(x,y)lower   (6)

where t is a distance from the lower pixel row Lp2 to the target pixel (pixel value g*(x,y)) in the X direction when the distance from the lower pixel row Lp2 to the upper pixel row Lp1 in the X direction is set to 1, and 0≦t≦1.

The image processor C carries out such calculation on the pixel columns (every y coordinate) in the region R of the combined image “plong*” passing through the low-pass filter, to extract the DC component from the region R (see FIG. 19). In the region R including areas above and below the pixel rows Lp1 and Lp2, respectively, as illustrated in FIG. 20, the DC components of these areas are defined as the pixel values g(x,y) of the pixels in these areas.

If the image processor C selects pixel rows Lp1 and Lp2 of pixels having significantly different pixel values g(x,y), the DC components acquired through linear interpolation will be significantly different from the actual DC components. Thus, it is preferred that the image processor C selects pixel rows Lp1 and Lp2 that have similar average pixel values g(x,y) of the pixels in the pixel rows Lp1 and Lp2, respectively.

With reference to FIG. 19, the image processor C subtracts the DC components extracted as described above from the region R of the combined image “plong*” passing through the low-pass filter, and removes the background of the region R of the combined image “plong*” passing through the low-pass filter, to extract the streaky components C_(L) residing or remaining in the region R. That is, the DC components g*(x,y) of the pixels in the background (pixel values g(x,y) for pixels in the areas above and below the pixel rows Lp1 and Lp2, respectively) are subtracted from the pixel values g(x,y) of the pixels in the region R in the combined image “plong*” passing through the low-pass filter, to extract the streaky components C_(L).

The image processor C adds the extracted streaky components C_(L) to the pixel values g(x,y) of the pixels corresponding to the combined image “plong*” (see FIG. 16), to remove the streaky components C_(L) from the combined image “plong*”.

In the removal of streaky components according to this embodiment (Step S6 in FIG. 7), the image processor C performs smoothing with a low-pass filter along the horizontal direction of the region R containing the streaky components C_(L) and assigned in an image p or the combined image “plong*”. The image processor C also performs streaky image extraction. That is, the image processor C performs interpolation in the vertical direction (X direction) on the smoothed image to extract the DC component as the interpolation image, subtracts the DC components from the smoothed image to extract the streaky components C_(L) as the streaky image (see FIG. 19), and adds the extracted streaky components C_(L) to the pixel values g(x,y) of the pixels corresponding to the image p or the combined image “plong*”, to remove the streaky components C_(L) from the image p or combined image “plong*”.

[Removal of Streaky Component (Modified): Summary]

However, the smoothing process which smooths the region R including the streaky component CL with a low-pass filter, etc. in the horizontal direction to form the smoothing image has the following problems.

For example, when there is a long subject structure B (structure existing in the subject, for example, metal piece such as a bolt attached to the bones) extending along the horizontal direction in the region R including the streaky component C_(L), and the subject structure B is captured within the region R including the streaky component C_(L), if the smoothing is performed in the region R including the streaky component C_(L) with the small-sized low-pass filter and the above-described extraction of the streaky image is performed to remove the streaky component from the region R including the streaky component C_(L), as shown in FIG. 21A, the portion of the subject structure B in which the width in the vertical direction is constant and the length in the horizontal direction is long blends in with the background and the outline disappears.

The low-pass filter smooths in the horizontal direction based on the pixel value of the target pixel and a plurality of pixels before and after the target pixel in the horizontal direction.

The size of the low-pass filter shows the number of pixels aligned in the horizontal direction to be referred to convert the pixel value of the target pixel.

The subject structure B disappearing as shown in FIG. 21A occurs when the size of the low-pass filter is smaller than the number of pixels in the horizontal direction in the image showing the subject structure B.

When the smoothing is performed with a low-pass filter with a size larger than the number of pixels in the horizontal direction in the image showing the subject structure B, and the above-described extraction of the streaky image is performed to remove the streaky components from the region R including the streaky component C_(L), as shown in FIG. 21B, the outline of the portion of the subject structure B which is long in the horizontal direction does not disappear and remains in the image.

However, if the size of the low-pass filter is made larger, it is not possible to sufficiently remove the streaky components from the image and the streaky components tend to remain in the image.

In view of the above, in addition to the smoothing process shown in FIG. 19, instead of using the low-pass filter with one size on the entire region R including the streaky component C_(L), the image processor C reflects on the image the smoothing with a larger-sized low-pass filter on pixels considered to be the subject structure extending in the horizontal direction in the region including the streaky component C_(L), than the low-pass filter used in the pixels other than the subject structure.

[Removal of Streaky Component (Modified): Smoothing]

The new smoothing process is described in detail below with reference to FIG. 22.

According to such smoothing process, a first smoothing image ph1 using a first low-pass filter with a large size on the region R including the streaky component C_(L) and a second smoothing image ph2 using a second low-pass filter with a small size on the region R including the streaky component C_(L) are generated.

Preferably, the low-pass filter with the small size is for example, a size suitable for extracting the streaky component.

Preferably, the low-pass filter with the large size has a size as large as possible, for example, a low-pass filter with a size close to the width of the images p1 and p2 in the horizontal direction.

The type of low-pass filter is not limited, but the present example uses a Gaussian filter which is one type of low-pass filter as the first and second low-pass filters.

The image processor C performs the streaky image extraction as shown in FIG. 19 on each of the first and second smoothing images ph1 and ph2. That is, the image processor C performs linear interpolation in the vertical direction on the first and second smoothing images ph1 and ph2 based on the pixels in the upper side and the lower side of the image than the range Rc including the streaky component C_(L), and generates the DC component (first and second interpolated image) of the first and second smoothing images ph1 and ph2. The image processor C also subtracts the DC component from each of the first and second smoothing images ph1 and ph2 to individually extract the first and second streaky images (streaky components) (not shown).

Further, the first and second streaky images are individually added to the region R including the streaky component CL, and first and second reference images with the streaky components CL removed from the region R are individually generated (not illustrated).

Then, a difference image ps is generated from a difference between a first reference image and a second reference image.

FIG. 21C is to be referred. FIG. 21C is a difference image subtracting the reference image (FIG. 21B) which is an image smoothed with the low-pass filter with a size larger than the subject structure B to remove the streaky component from the reference image (FIG. 21A) which is an image smoothed with the low-pass filter with a size smaller than the subject structure B to remove the streaky component.

As shown in FIG. 21C, the difference image of the reference images using large and small low-pass filters can clearly extract the subject structure B which has a size in between the large and small low-pass filters.

Therefore, in the smoothing shown in FIG. 22, the pixels considered to be the subject structure extending in the horizontal direction in the region R including the streaky component C_(L) are extracted from the obtained difference image ps.

That is, the image processor C compares the pixel values of all pixels in the difference image ps with a predetermined threshold for extracting the subject structure. The plurality of pixels exceeding the threshold are extracted as “pixels considered to be the subject structure”.

Preferably, the threshold can be set to any value with an input unit provided in the image processor C.

As described above, according to the new smoothing, the smoothing process reflects the image smoothing performed on the pixels considered to be the subject structure extending in the horizontal direction in the region R including the streaky component C_(L) using a low-pass filter with a larger size than the low-pass filter used for the pixels other than the subject structure.

As for the pixels other than the subject structure in the region R including the streaky component C_(L), the pixel value of the above-described second smoothing image ph2 is applied. As for the plurality of pixels considered to be the subject structure in the region R including the streaky component C_(L), the pixel values blending (combining) the pixel values of the first and second smoothing images ph1 and ph2 at a blend ratio A according to each pixel value in the difference image are applied. By generating a combined smoothing image pg of the region R including the streaky component C_(L) according to the pixel values as applied above, the smoothing is substantially performed. The smoothing using the low-pass filter larger than the low-pass filter used on the pixels other than the subject structure is performed on the pixels showing the subject structure, and such smoothing is reflected on the image.

The relation between pixel values in the difference image ps showing the pixel values of the plurality of pixels considered to be the subject structure and the blend ratio A is described.

The pixel values in the difference image ps showing the pixel values of the plurality of pixels considered to be the subject structure are larger than the threshold to extract the subject structure from the difference image ps. Therefore, such threshold is to be the lower limit and the maximum value among the pixel values in the difference image ps showing the pixel values of the plurality of pixels considered to be the subject structure is to be the upper limit.

Then, the blend ratio A=0 when the pixel value is the lower limit value (α), the blend ratio A=1 when the pixel value is the upper limit value (β) and the blend ratio A=(γ−α)/(β−α) for the pixel value in between (γ). With this, the blend ratio A is to be within the range of 0 to 1.

Then, the blend ratio A is calculated separately from each pixel value in the difference image regarding the plurality of pixels considered to be the subject structure.

Further, the pixel value is calculated from the following equation regarding each of the plurality of pixels considered to be the subject structure.

pixel value of the pixel with the same position as the pixel considered to be the subject structure in the first smoothing image ph1×A+pixel value of the pixel with the same position as the pixel considered to be the subject structure in the second smoothing image ph2×(1−A)

As for the pixel other than the plurality of pixels considered to be the subject structure, the pixel value of the pixel with the same position in the second smoothing image ph2 is employed as is.

The combined smoothing image pg is generated according to the above calculation.

In the region R including the streaky component C_(L), when the pixel value blending (combining) the pixel values of the first and second smoothing images ph1 and ph2 are assigned to the plurality of pixels considered to be the subject structure, the following can be performed in advance. That is, the calculation for the first and second smoothing images ph1 and ph2 can be performed again, the weighting for the plurality of pixels considered to be the subject structure can be lowered (the coefficient in the low-pass filter for the plurality of pixels considered to be the subject structure can be reduced), the region R can be smoothed again, and the pixel values blending (combining) the pixel values of the new first and second smoothing images ph1 and ph2 can be assigned.

That is, when new smoothing is performed, if the pixel considered to be the subject structure is the target pixel or is not the target pixel but is the pixel included in the smoothing calculation (pixel adjacent to or near the target pixel) the coefficient of the low-pass filter used on the pixel considered to be the subject structure reduced to perform smoothing again, and the pixel value of the pixel considered to be the subject structure in the newly obtained first and second smoothing images can be blended to generate the combined smoothing image pg.

[Removal of Streaky Component (Modified): Streaky Image Extraction]

After the smoothing process is performed, the streaky image extraction is performed similar to the above-described FIG. 19.

That is, the image processor C performs vertical interpolation in the vertical direction (X-direction) on the combined smoothing image pg to extract the DC component as the obtained interpolation image and subtracts the DC component from the combined smoothing image pg to extract the streaky component C_(L) as the streaky image. The extracted streaky component C_(L) is added to the pixel value g(x,y) of each pixel corresponding to the image p and the combined image “plong*” to remove the streaky component C_(L) from the image p and the combined image “plong*”.

[Removal of Streaky Component (Modified): Other Smoothing Process]

According to the above smoothing process, the first smoothing image ph1 and the second smoothing image ph2 are combined to generate the combined smoothing image pg. The smoothing process is not limited to such combining process and other process can be performed.

Specifically, the image processor C is provided with a storage including a non-volatile memory or a HDD to store data of low-pass filters with a plurality of sizes (for example, low-pass filters with a plurality of sizes between the sizes of the second low-pass filter and the first low-pass filter), and table data showing the suitable relation between the low-pass filter with the plurality of sizes and the pixel value of the pixel considered to be the subject structure in the difference image ps.

Then, the low-pass filter with the suitable size is selected in the unit of the plurality of pixels considered to be the subject structure from the pixel value of the plurality of pixels considered to be the subject structure extracted from the difference image ps, and with reference to the table data in the storage.

Then, as for the plurality of pixels considered to be the subject structure, the region R including the streaky component C_(L) is smoothed based on the low-pass filter with each selected size. As for the pixels other than the plurality of pixels considered to be the subject structure, the region R including the streaky component C_(L) is smoothed based on the second low-pass filter.

As described above, smoothing can be performed on the plurality of pixels considered to be the subject structure and the pixels other than the above using low-pass filters with different sizes to perform composite smoothing.

The streaky image extraction similar to the above-described FIG. 19 is performed after such composite smoothing also.

[Removal of Streaky Component (Modified): Vertical Smoothing]

As described above, when smoothing is performed using a low-pass filter with a large size, the effect of removing the streaky component reduces.

Therefore, horizontal streaky components may remain in the image of the subject structure formed with the plurality of pixels considered to be the subject structure included in the image after streaky component extraction. The same can be said for smoothing generating the combined smoothing image pg and the composite smoothing.

Therefore, the image processor C performs smoothing in the vertical direction on all or a portion of the plurality of pixels considered to be the subject structure included in the image of the region R in which the streaky components are removed by the above-described smoothing processes.

Smoothing in the vertical direction can be performed using any well-known smoothing filter. Here, smoothing using a minimizing filter is described.

The minimizing filter is a filter which converts the pixel value of target pixel to the value with the lowest pixel value among the target pixel and the plurality of pixels aligned above and below the target pixel in the vertical direction.

As shown in FIG. 23, when smoothing is performed with the minimizing filter, the change of the pixel value (signal value) of the pixel aligned along the coordinates in the vertical direction becomes smooth in the smoothed corrected region, and the significance of the remaining streaky components can be reduced.

The smoothing in the vertical direction can be performed on all of the plurality of pixels considered to be the subject structure. Preferably, the pixels smoothed with the large-sized low-pass filter are to be the target. The streaky components tend to remain in such pixel.

Therefore, a threshold to determine the target of smoothing in the vertical direction is set for the pixel values of the plurality of pixels considered to be the subject structure in the difference image ps, and the pixel as the target of smoothing in the vertical direction is determined according to whether the value exceeds the threshold.

Such threshold is set with a value larger than the above-described threshold to extract the subject structure. The threshold to determine the target of smoothing in the vertical direction can be set freely with the input unit provided in the image processor C.

In this embodiment, the image processor C removes the streaky components as described above to suitably correct the combined image “plong*” or images p1 and p2, to precisely remove the streaky components C_(L) residing or remaining in the combined image “plong*” or the images p1 and p2.

As a result of extracting the region R, which contains the streaky components C_(L), from an image p or the combined image “plong*”, and adding the streaky components C_(L) extracted from the region R through the processes illustrated in FIG. 19 to the pixel values g(x,y) of the pixels corresponding to the image p or the combined image “plong*” (see FIG. 16), as described above, the areas inside or outside the boundary of the region R in the image p or the combined image “plong*” and/or the pixel rows Lp1 and Lp2 selected as described above could include a fluctuation in pixel values.

In such a case, in the process of adding the streaky components C_(L) extracted as described above to the image p or the combined image “plong*” from which the streaky components are removed, the products of the streaky components C_(L) and a coefficient are added to the image p or combined image “plong*” so as to prevent the fluctuation (or significantly reduce it to a non-visible level) and smooth the areas of the image p and the combined image “plong*” above and below the fluctuation (i.e., smoothing).

[Adjustment of Contrast and Granularity—Step S7]

Even after image correction is carried out as described above to remove the structural components C_(S) and the streaky components C_(L) (Steps S3 and S6) from the combined image “plong*” or images p1 and p2 (hereinafter, collectively referred to as combined image “plong*”), the contrast and granularity of the areas in the combined image “plong*” from which the structural components C_(S) and the streaky components C_(L) are removed may have contrast and granularity different from those of other areas in the combined image “plong*”.

After the image processor C removes the structural components C_(S) and the streaky components C_(L) from the combined image “plong*”, as described above, the contrast and granularity of the overall combined image “plong*” can be adjusted to matched values (Step S7 in FIG. 7). That is, the contrast and granularity of the areas of the combined image “plong*” from which the structural components C_(S) and the streaky components C_(L) are removed are matched to the contrast and granularity of the other areas in the combined image “plong*” (in particular, the periphery of the removed structural components C_(S) and streaky components C_(L)). Such image processing can be performed to match the contrast and granularity of the different areas in the combined image “plong*”, making the areas in the combined image “plong*” from which the structural components C_(S) and the streaky components C_(L) are removed indistinguishable from the other areas.

The contrast and granularity can be adjusted so that the horizontal lines above and below the seam of combined images have similar frequency components, for example. Specifically, (1) high-frequency components above the seam are blurred or smoothed; (2) an unsharp mask is applied below the seam to enhance the high-frequency components; and (3) the high-frequency components above and below the seam are measured and adjusted to match each other. The process returns to step (1) and repeated, as necessary. In step (3), a Fourier transform spectrum or other statistical indices may be used as a measurement index.

In another scheme, the amplification factors of the contrast and granularity can be preliminarily defined in each area that contains structural components C_(S) and streaky components C_(L) caused by the projection of the front radiographic image capturing device Pb in the image p captured by the rear radiographic image capturing device Pa; the areas in the image p from which the structural components C_(S) and the streaky components C_(L) are removed as described above are resolved into low, intermediate, and high frequency image components; and the product of the intermediate frequency image components and the amplification factor of contrast, the product of the high frequency image components and the amplification factor of granularity, and these products are added to the low frequency image components, to achieve uniform contrast and granularity.

The amplification factors of the contrast and granularity may be 1 or more or less than 1. An amplification factor of 1 or more enhances contrast and granularity, whereas an amplification factor of less than 1 smooths contrast and granularity. The high frequency information removed from the image after adjustment can be recovered through the use of a Wiener filter. Such a technique is effective in making an indistinguishable seam between images having different qualities.

[Generation of Long Image]

As described above, the image processor C corrects the combined image “plong*” through removal of structural components and streaky components and adjusts the contrast and granularity, as required, to acquire a combined image “plong*” equivalent to a long image “plong”, such as that illustrated in FIG. 24. Thus, the image processor C can generate a long image “plong” through image correction on the combined image “plong*”, as described above.

As described above, in the generation of a typical long image “plong” through combination of images p1 and p2 (or images p1 to p3), the connecting area (overlapping area) of the images p contain an image captured by the radiographic image capturing device Pb loaded in the front position in the holder 51 a of the capturing stand 51A (for example, the image captured by the front radiographic image capturing device Pb in FIG. 6). In contrast, in the connecting step (Step S5) in the image correction process according to this embodiment (see FIG. 7), the connecting area (overlapping area) of the images p contains an image p captured by the radiographic image capturing device Pa loaded in the rear position in the holder 51 a of the capturing stand 51A.

Alternatively, in this embodiment, a long image “plong” can be generated in accordance with the process of generating a typical long image “plong”.

[Segmentation—Step S8]

In this embodiment, the image processor C corrects the combined image “plong*” through removal of structural components and streaky components, as described above, adjusts the contrast and granularity, as required, and segments the processed combined image “plong*” into images p1 to p3 (Step S8 in FIG. 7). To differentiate the images p1 to p3 captured by the radiographic image capturing devices P1 to P3, respectively, loaded in the holder 51 a of the capturing stand 51A, the images acquired through segmentation of the processed combined image “plong*” will hereinafter be referred to as images p*1 to p*3.

In the segmentation (Step S8), the image processor C segments the processed combined image “plong*” at the bottom edges of the images p1 and p2, as illustrated in FIG. 25A, prior to combination (see FIGS. 13A and 13B) to generate images p*1 to p*3. Simple segmentation of the processed combined image “plong*” could cause loss in the image p2 in the overlapping area of the images p1 and p2, which are combined after the concentration correction (Step S3 in FIG. 7) and the adjustment of the position and enlargement factor (Step S4). Similarly, a portion of the image p3 could be lost in the overlapping area of the images p2 and p3 that are combined.

Among the images p*1 to p*3 generated through the segmentation of the processed combined image “plong*,” a portion of the image p2 corresponding to the overlapping area of the combined images p1 and p2 and a portion of the image p3 corresponding to the overlapping area of the combined images p2 and p3 are respectively added to the top ends of the images p*2 and p*3, which are generated through segmentation.

In this embodiment, the images p*1 and p*2 generated by the image processor C through segmentation of the combined image “plong*”, as illustrated in FIG. 25B, are derived from the images p1 and p2 through removal of the structural components C_(S) and the streaky components C_(L) (and the adjustment of the contrast and granularity, as required).

In other words, the structural components C_(S) and the streaky components C_(L) can be precisely removed from the images p1 and p2 acquired by the rear radiographic image capturing devices P1 and P2, respectively, loaded in the holder 51 a of the capturing stand 51A. Since the segmented image p*3 does not contain structural components C_(S) and streaky components C_(L) in the first place, the segmented image p*3 is identical to the original image p3.

[Advantageous Effects]

In the radiographic image capturing system 50 according to this embodiment as described above, the image processor C can remove the structural components C_(S) and the streaky components C_(L) (see FIGS. 12, 29A, and 29B) caused by the front radiographic image capturing device Pb projected on the image p acquired by the rear radiographic image capturing device Pa loaded in the holder 51 a of the capturing stand 51A for capturing a long image by one-shot exposure (see FIG. 6).

By image correction on the image p, the images p acquired through capturing of a long image by one-shot exposure can be precisely corrected, and images p*1 to p*3 (see FIG. 25B) can be acquired through precise removal of the structural components C_(S) and the streaky components C_(L) from the corrected images p. The images p*1 to p*3 can be combined to precisely generate a long image “plong” (see FIG. 24).

In the embodiment described above, as illustrated in FIG. 20, the pixel row Lp1 having a width of one pixel is selected from the image p1, and the pixel row Lp2 having a width of one pixel is selected from the image p2. The pixel rows Lp1 and Lp2 are linearly interpolated by expression (6) to calculate the DC components, which are background components of the region R required for the removal of streaky components. Unfortunately, the removal of the streaky components from each of the images p1 and p2, as described, precludes the selection of at least the pixel row Lp2 having a width of one pixel.

In such a case, for example, the streaky components can be removed from each of the images p1 and p2 as in the embodiment described above using data on a pixel row having a width of one pixel at the top of the image p2 for the removal of the streaky components from the image p1 and using data on a pixel row having a width of one pixel at the top of the image p3 for the removal of the streaky components from the image p2.

For example, during removal of the streaky components from the image p1, pixel rows Lp1 and Lp2 both having a width of one pixel may be selected from the image p1 above a range Rc (see FIG. 20), and the pixel row Lp2 can be presumed to be present in the image p1 below the range Rc, as illustrated in FIG. 20. In this way, the streaky components can be removed from each of the images p1 and p2 as in the embodiment described above.

According to the modified smoothing process included in the removal of the streaky components, the image processor C of the radiation image capturing system 50 reflects on the image the smoothing using the large-sized low-pass filter in the horizontal direction on the pixels showing the subject structure B extending in the horizontal direction and existing in the region R which is set in the image and includes the streaky components compared to the low-pass filter used for the pixels other than the pixels showing the subject structure B.

Therefore, the streaky components can be effectively removed for the pixels other than the pixels showing the subject structure B while preventing loss of the outline of the subject structure B existing in the region R.

According to the modified streaky component removal, the subject structure extraction is included. Specifically, smoothing is performed on the region R which is set in the image and includes the streaky components using first and second low-pass filters with different sizes in the horizontal direction. From each of the individually obtained first and second smoothing images ph1 and ph2, the DC components (first and second interpolated image) are subtracted to extract the first and second streaky images. The first and second streaky images are individually added to the region R including the streaky component to obtain the first and second reference images. The subject structure is extracted from the difference image ps of the first and second reference images.

Therefore, the subject structure included in the region R including the streaky component can be accurately extracted. With this, accurate smoothing can be performed and the loss of the outline of the subject structure B can be effectively prevented.

According to the modified smoothing of the streaky component removal, the pixel value smoothed with the first low-pass filter and the pixel value smoothed with the second low-pass filter are combined at a ratio corresponding to the magnitude of the pixel value of the plurality of pixels composing the subject structure extracted from the difference image ps by the subject structure extraction. The pixel value of the plurality of pixels composing the subject structure in the region including the streaky component is corrected and this is substantially the same as smoothing with a low-pass filter larger than the low-pass filter used for the pixels other than the plurality of pixels showing the subject structure.

Therefore, the smoothing on the plurality of pixels composing the subject structure using a low-pass filter with a larger size can be reflected on the image and the loss of the outline of the subject structure B can be effectively prevented.

According to the modified smoothing of the streaky component removal, when the plurality of pixels composing the subject structure in the region including the streaky component is smoothed using a low-pass filter with a size corresponding to the size of the pixel value of the plurality of pixels composing the subject structure extracted from the difference image ps in the subject structure extraction, the plurality of pixels composing the subject structure can be smoothed using a low-pass filter with a suitable size, and the loss of the outline of the subject structure B can be effectively prevented.

According to the modified streaky component removal, smoothing in the vertical direction is performed on some or all of the pixels showing the subject structure B extending in the horizontal direction including the region R including the streaky component after removing the streaky components with the streaky image extraction. Therefore, the reduction of the effect of removing the streaky components using the low-pass filter with a large size can be reduced.

[Images without Projection of Structural Component]

Depending on the structure of the front radiographic image capturing device Pb (see FIG. 6) loaded in the holder 51 a of the capturing stand 51A, the image p captured by the rear radiographic image capturing device Pa could contain the streaky components C_(L) without the structural components C_(S) or with structural components C_(S) which are hardly visible.

In such a case, as in the embodiment described above, the images p1 to p3 can be combined to remove the streaky components, or the streaky components can be removed from each of the individual images p1 and p2 without combination of the images p1 to p3. In such a case, the Steps S1 and S2 in the flow chart illustrated in FIGS. 7 and 26, for example, are unnecessary, and thus the calibration image “pcal” is also unnecessary. The removal of the streaky components is then carried out as illustrated in FIG. 19.

In the removal of streaky components from a combined image “plong*” generated through the combination of the images p1 to p3 or from each of the individual images p1 and p2 without combination of the images p1 to p3, image processing is carried out as described above to match (enhance or smooth) the contrast and granularity in the areas of the combined image “plong*” or the images p1 and p2 from which the streaky components C_(L) are removed to the other areas of the combined image “plong*” or the images p1 and p2 (in particular, the periphery of the removed structural components C_(S) and streaky components C_(L)).

Through such configuration, areas in the combined image “plong*” or the images p1 and p2 from which the structural components C_(S) and the streaky components C_(L) are removed can be indistinguishable from other areas, as described above.

The present invention is not limited to the above embodiments and modifications, and can be suitably changed without leaving the scope of the present invention. 

What is claimed is:
 1. A radiographic image capturing system comprising: a capturing stand which includes a holder which is able to hold a plurality of radiographic image capturing devices; a radiation irradiator which is able to irradiate the radiographic image capturing devices loaded in the holder at once with radiation; and an image processor which generates a plurality of images based on image data acquired by the radiographic image capturing devices, wherein, an end of a front radiographic image capturing device overlaps in an anteroposterior direction with an end of a rear radiographic image capturing device in the holder in view from the radiation irradiator, the front radiographic image capturing device being a radiographic image capturing device close to the radiation irradiator among the radiographic image capturing devices loaded in the holder, the rear radiographic image capturing device being a radiographic image capturing device remote from the radiation irradiator among the radiographic image capturing devices loaded in the holder, the image processor removes a streaky component residing in the generated image to correct the image, the removal of the streaky component includes, forming a smoothed image by smoothing with a low-pass filter to perform smoothing in a horizontal direction on a region including the streaky component set in the image, and subtracting an interpolation image obtained by interpolation in a vertical direction in a region including the streaky component on the smoothing image to extract a streaky image from the smoothing image and adding the streaky image on the region including the streaky component set in the image to remove the streaky component, wherein the smoothing includes reflecting smoothing on pixels showing a subject structure, which exists in the region including the streaky component set in the image and extends in a horizontal direction, using a low-pass filter with a size larger in the horizontal direction compared to pixels other than pixels showing the subject structure.
 2. The radiographic image capturing system according to claim 1, wherein, the removal of the streaky component includes, smoothing using each one of a first low-pass filter and a second low-pass filter with different sizes in the horizontal direction on the region including the streaky component set in the image to respectively obtain a first smoothing image and a second smoothing image, obtaining a first interpolation image and a second interpolation image by interpolating in the vertical direction the first smoothing image and the second smoothing image, and subtracting each one of the first interpolating image and the second interpolating image from the first smoothing image and the second smoothing image, respectively, to extract a first streaky image and a second streaky image; and adding each of the first streaky image and the second streaky image to the region including the streaky component to obtain a first reference image and a second reference image, subtracting one of the first reference image or the second reference image from the other to obtain a difference image, and extracting the subject structure from the difference image.
 3. The radiographic image capturing system according to claim 2, further comprising a storage to store a plurality of low-pass filters with different sizes in the horizontal direction, wherein, smoothing is performed on a plurality of pixels composing the subject structure in the region including the streaky component with the low-pass filter having a size corresponding to a size of a pixel value of the plurality of pixels composing the subject structure extracted from the difference image in the subject structure extraction.
 4. The radiographic image capturing system according to claim 2, wherein, the smoothing includes correcting a pixel value of the plurality of pixels composing the subject structure in the region including the streaky component by combining a pixel value smoothed with the first low-pass filter and a pixel value smoothed with the second low-pass filter at a ratio corresponding to a size of the pixel value of the plurality of pixels composing the subject structure extracted from the difference image in the subject structure extraction.
 5. The radiographic image capturing system according to claim 1, wherein, the removal of the streaky component includes smoothing in the vertical direction on all or some of the pixels showing the subject structure extending in the horizontal direction included in the region including the streaky component from which the streaky component is removed in the streaky image extraction.
 6. The radiographic image capturing system according to claim 1, wherein, the streaky component occurs due to the plurality of radiation image capturing devices overlapping in the anteroposterior direction.
 7. An image processor which generates a plurality of images based on image data acquired by irradiating radiographic image capturing devices at once with radiation in a state in which an end of a front radiographic image capturing device overlaps in an anteroposterior direction with an end of a rear radiographic image capturing device in a holder in view from a radiation irradiator, the front radiographic image capturing device being a radiographic image capturing device close to the radiation irradiator among the radiographic image capturing devices loaded in holders of a capturing stand, the rear radiographic image capturing device being a radiographic image capturing device remote from the radiation irradiator among the radiographic image capturing devices loaded in the holders, the image processor comprising: a processor, wherein the processor removes a streaky component residing in the generated image to correct the image, wherein the removal of the streaky component includes, forming a smoothed image by smoothing with a low-pass filter to perform smoothing in a horizontal direction on a region including the streaky component set in the image, and subtracting an interpolation image obtained by interpolation in a vertical direction in a region including the streaky component on the smoothing image to extract a streaky image from the smoothing image and adding the streaky image on the region including the streaky component set in the image to remove the streaky component, wherein the smoothing includes reflecting smoothing on pixels showing a subject structure, which exists in the region including the streaky component set in the image and extends in a horizontal direction, using a low-pass filter with a size larger in the horizontal direction compared to pixels other than pixels showing the subject structure.
 8. An image processing method performed by an image processor which generates a plurality of images based on image data acquired by irradiating radiographic image capturing devices at once with radiation in a state in which an end of a front radiographic image capturing device overlaps in an anteroposterior direction with an end of a rear radiographic image capturing device in the holder in view from a radiation irradiator, the front radiographic image capturing device being a radiographic image capturing device close to the radiation irradiator among the radiographic image capturing devices loaded in holders of a capturing stand, the rear radiographic image capturing device being a radiographic image capturing device remote from the radiation irradiator among the radiographic image capturing devices loaded in the holders, the image processing method comprising: removing a streaky component residing in the generated image to correct the image, the removal of the streaky component includes, forming a smoothed image by smoothing with a low-pass filter to perform smoothing in a horizontal direction on a region including the streaky component set in the image, and subtracting an interpolation image obtained by interpolation in a vertical direction in a region including the streaky component on the smoothing image to extract a streaky image from the smoothing image and adding the streaky image on the region including the streaky component set in the image to remove the streaky component, the smoothing includes reflecting smoothing on pixels showing a subject structure, which exists in the region including the streaky component set in the image and extends in a horizontal direction, using a low-pass filter with a size larger in the horizontal direction compared to pixels other than pixels showing the subject structure. 